In a gasoline engine, atomization of fuel is not completely effected at a carburetor. Therefore, the fuel, which is not atomized, is introduced into combustion chambers in a liquid condition along the inner surface of an intake passageway of the engine. In this case, the fuel can not be uniformly supplied to each cylinder of the engine, and the fuel can not be uniformly supplied to every portion of a cylinder. This causes an unstable combustion and a low engine efficiency, as well as a large emission of HC and CO components.
In prior arts, various systems are used for atomizing fuel, wherein an additional flow of air from the outside of the engine is ejected into an intake passageway of the engine under the action of vacuum pressure therein, in order to generate turbulence of the flow of the combustible mixture or to blow off a fuel contacting the inner wall of the intake passageway (Japanese Laid-Open Utility Model Registration Publication No. 52-57131, Japanese Laid-Open Patent Publication No. 50-18825, Japanese Utility Model Publication No. 51-12578 and Japanese Utility Model Publication No. 51-10245). These prior arts, however, suffer from a disadvantage that it is difficult to maintain a predetermined constant air-fuel ratio of the combustible mixture directed to the combustion chambers of the engine, since the vacuum pressure in the intake passageway, which corresponds to the amount of the externally introduced air, is changed in accordance with the load of the engine.